Aerial systems



y 1959 E. D. FARA'MER ET AL 2,395,132

AERIAL. SYSTEMS,

Filed Aug. 15, 1957 1 Q mvzuroRs Fus /LL A/ ERMQR Dav/ Jasepq Mr Gaunt our aga dim; Jim

-' Patented July 14, 1959 States Patent Ofiice 2,895,132 AERIAL SYSTEMS Eugene Dillon Farmer and Denis Joseph McConalogue, :London, England, assignors to The General Electric Company Limited, London, England Application August 15, 1957, Serial No. 678,361

Claims priority, application Great Britain r August 17,1956

. 4 Claims. or; 343-761) This invention relates to aerial systems and is more particularly concerned with radar aerial systems of the kind'that is arranged to produce a conical scan.

QAknown construction of radar aerial system of this kind comprises a dish-shaped metal reflector which has areflecting surface that lies on that part of a paraboloid cut olf by'a plane at right angles to the axis of the paraboloid' and a primary aerial, such 'as a dipole, which is caused to" nutate about the axis of the paraboloid so as to produce the desired conical scan. The main lobe of the radiation pattern of such an aerial system subtends a relatively narrow angle although there are also a number of side lobes; these being arranged to be of smaller amplitude than the main lobe. It is often found however that, due to the asymmetry of such arrangements, the radiation pattern when the primary aerial is in any particular position has side lobes on either side of the main lobe that are of unequal amplitude.

In certain applications this inequality of side lobes is undesirable and it is one object of the present invention to provide an aerial system which at least partially compensates for the asymmetry.

According to the present invention, a radar aerial system comprises a paraboloidal reflector, a feeder waveguide which is mounted for rotation about its longitudinal axis, a further length of waveguide which constitutes an extension of the feeder waveguide but which is offset at an angle to the feeder waveguide, a member projecting into the said further length of waveguide, and a primary aerial which comprises at least a dipole and which is mounted on said member beyond the open end of the said further length of waveguide so as to lie partially on either side of the member, the arrangement being such that rotation of the feeder waveguide causes the primary aerial to nutate about said axis in the region of the focus of the reflector while the shape and/ or position of the said member with respect to the said further length of waveguide results in unequal coupling between the feeder waveguide and parts of the primary aerial on either side of the said member so as, at least in part, to compensate for the mechanical asymmetry of the aerial system that would otherwise tend to produce unequal side lobes.

The longitudinal axis of the feeder waveguide may be coincident with the axis of the reflector.

One example of a radar aerial system in accordance with the present invention will now be described with reference to the three figures of the accompanying drawing in which Figure 1 shows the general assembly of the aerial system partially in section;

Figure 2 shows a sectional view of part of the aerial system in more detail; and

Figure 3 shows a cross-section at the line III-III in Figure 2.

Referring now to Figure 1 of the accompanying drawing, the aerial system comprises a dish-shaped reflector 1 that has a paraboloidal reflecting surface 2, the edge 3 of the reflector 1 lying in a plane that is at right angles to the axis 4 of the paraboloid. A primary aerial 5 is formed by a pair of dipoles 6 and 7 which are mounted, in a manner that will be apparent hereinafter, slightly off the axis 4 of the paraboloid so that they can nutate about that axis in the region of the focus of the reflector 1.

A brass feeder waveguide 8 of uniform rectangular cross-section projects through the reflector 1, the longitudinal axis of this waveguide 8 being coincident with the axis 4. A further length of waveguide 9, that is integral with the feeder waveguide 8, constitutes an-extension of the feeder waveguide and has its longitudinal axis 10 inclined at an angle of 7 to that of the feeder waveguide. This further length of waveguide 9 is also of rectangular cross-section but is uniformly tapered along its length, in both width and depth, away from the feeder waveguide 8.

Referring now also to Figures 2 and 3, a brass member 11 projects a short distance into the open end 12 of the further length of waveguide 9, this member 11 being secured to the broader walls, such as the wall 13, of the further length of waveguide 9, for example by soldering Apart from the portion 14 of the member 11, the significance of which will be explained hereinafter, the member 11 is planar and is mounted so that the longitudinal axis 10 of the waveguide 9 lies in the plane of the member 11.

The dipoles 6 and 7 are formed by two brass rods mounted on the member 11 so that each projects through the member and lies equally on either side thereof, the axes of these two rods being perpendicular to the said plane of the member 11. The dipole 7 is in fact located a short distance beyond the open end 12 of the further length of waveguide 9 while the other dipole 6 which is of slightly greater length is located further from this open end 12. As previously mentioned, the pair of dipoles 6 and 7 constitute the primary aerial 5 which during transmission, for example, is excited by energy fed thereto by way of the feeder waveguide 8 and the further length of waveguide 9.

The end of the feeder waveguide 8 which lies behind the reflector 1 is connected to a coaxial transmission line 15 by way of a transformation which is shown diagrammatically in Figure 1 by the rectangle 16. This line 15 is arranged to be supplied by the aerial 17 through a rotating joint 18. The assembly formed by the coaxial transmission line 15, the transformation 16, the feeder waveguide 8, the further waveguide 9 and the primary aerial 5 are arranged for rotation about the axis 4 and in Figure 1, this assembly is shown as being supported relative to the reflector 1 by a bearing 19. An electric motor 20 is arranged to drive this assembly through gearing 21 so as to cause it to rotate about the axis 4.

The reflector 1 has a central circular hole 22 through which passes the feeder waveguide 8. In fact a member 23 is secured to the feeder waveguide 8 so as to rotate therewith the member 23 partially filling the hole 22 and having a reflecting surface 24 which forms a continuation of the paraboloidal surface 2.

In order, during transmission, to prevent energy being reflected back from the reflector 1 to the primary aerial 5 so as further to excite that aerial and thereby cause multiple transmissions, a small additional reflector 25 is provided in known manner. This additional reflector 25 is annular in shape and embraces the feeder waveguide 8 to which it is secured, its reflecting surface 26 lying on the surface of a sphere the centre of which is on the axis 4.

In order to prevent the aerial system having a radiation pattern with unequal side lobes, as previously discussed, the member 11 on which the two dipoles 6 and 7 are mounted is not completely planar, the portion 14 thereof that lies within the further length of waveguide 9 being bent away from the longitudinal axis 10 of that waveguide. In one construction, for equal side lobs, this portion 14 is inclined at an angle of 1O A to the longitudinal axis 10, the resulting unequal coupling between the feeder waveguide 8 and the two halves of the primary aerial on either side of the member 11 compensating for the mechanical asymmetry of the aerial system.

Instead of bending the member 11, the same effect may be obtained by moving the whole member laterally so that it is parallel to, but spaced a distance from, the longitudinal axis 10 of the further length of waveguide 9.

It is to be understood that the present invention, although discussed above with reference to a transmitting aerial system is equally applicable to a receiving aerial system. 7

What we claim is:

1. A radar aerial system comprising a paraboloidal reflector, a feeder waveguide which is mounted for rotation about its longitudinal axis, a further length of waveguide which constitutes an extension of the feeder waveguide but .which is offset at an angle to the feeder Waveguide, a member projecting into the said further length of waveguide, a primary aerial which comprises at least a dipole and which is mounted on said member the focus of the reflector while the unequal coupling between the feeder waveguide and parts of the primary aerial on either side of the said member compensates, at least in part, for the mechanical asymmetry of the aerial system that would otherwise tend to produce unequal side lobes.

2. A radar aerial system according to claim 1, wherein the longitudinal axis of the feeder waveguide is coincident with the axis of the reflector.

3. A radar aerial system according to claim 1 wherein a portion of the said member is inclined to the longitudinal axis of the further length of waveguide while the remainder of that member which constitutes the major portion thereof is planar and is mounted so that the longitudinal axis of the further waveguide lies in the plane of the said major portion of the member.

4. A radar aerial system according to claim 1 wherein the primary aerial is formed by two dipoles.

References Cited in the file of this patent UNITED STATES PATENTS 2,605,419 Van Atta July 29, 1952 

